Internal combustion engines, in particular diesel and gasoline engines, are frequently equipped with turbochargers. A turbocharger operates by compression of the intake airflow into the engine in order to achieve more power. In particular, a predetermined power can be generated by a turbocharged engine with a smaller displacement volume and thus smaller size and less weight, thereby achieving an increased specific power and a reduction of fuel consumption.
In general, turbochargers are driven by the exhaust flow of the internal combustion engine. To this end, a turbocharger comprises a turbine arranged in the exhaust flow of the internal combustion engine, driving a compressor for compressing the intake airflow of the engine via a connecting drive shaft.
Recently, multi-stage sequential turbocharging has become popular. A regulated two-stage turbocharging system comprises a low-pressure (LP) stage for peak power and a high-pressure (HP) stage for fulfilling the back pressure requirements for driving exhaust gas recirculation, which is needed for NOx pollutant emission reduction. Moreover, the HP turbine usually is smaller and more responsive than the LP turbine. The HP and LP turbines are arranged sequentially in the exhaust flow of the internal combustion engine, the LP turbine being located downstream the HP turbine. The LP and HP compressors are arranged sequentially as well, the HP compressor being located in the intake airflow downstream the LP compressor.
The exhaust flow and/or the intake airflow are controlled by one or more bypass valves located in branches of the exhaust and/or intake system, which are parallel to the respective turbine and/or compressor. In particular, the exhaust flow may be controlled by a bypass valve of the HP turbine and/or a wastegate for bypassing the LP turbine. With the bypass valve closed, the respective turbine is driven maximally, while with the bypass valve partially or fully opened, the parallel branch is passed by at least part of the exhaust flow, the respective turbine being driven at a reduced rate. Similarly, the intake airflow may be controlled by a compressor bypass valve of the HP compressor. The bypass valves ensure a smooth operation of the engine and also ensure respecting various further constraints, concerning for example exhaust composition, compressor outlet temperature and turbine inlet temperature, as well as avoiding turbocharger surge or overspeed.
The bypass valves may be controlled actively, for example, electrically or by vacuum, and may comprise a position feedback sensor. As the HP turbine bypass valve is critical to emissions control, it is usually actively controlled and equipped with a position feedback sensor. The compressor bypass valve usually is passive, i.e. it opens or closes due to the pressure difference across it, having only two possible positions, which are the fully open and the fully closed positions. The amount of pressure difference required to operate the compressor bypass valve is determined by the design of the valve, for example, by the stiffness of a spring acting on the valve. The compressor bypass valve may or may not be equipped with a position feedback sensor. The wastegate is usually also actively actuated, however, for reduction of cost and complexity, it often does not comprise a position feedback sensor.
The active valves usually have a default or “failsafe” position into which they move when there is no vacuum or electrical supply. The failsafe position normally is either fully open or fully closed. The default setting is determined by factors such as safety and engine power requirements at altitude. However, due to a variety of reasons, the low-pressure turbine bypass valve may fail, being stuck in the fully closed or in the fully open position, for example. It would be desirable to be able to detect such failure of the wastegate, without a position feedback sensor involving increased cost and complexity.
The inventors have recognized the issues with the above approach and herein provide a method to at least partly address them. In one embodiment, a method for operating a turbocharger arrangement of an internal combustion engine, the turbocharger arrangement comprising a low-pressure and a high-pressure turbocharging stage arranged sequentially, the low-pressure turbo-charging stage comprising a low-pressure turbine with a sensorless low-pressure turbine bypass valve, comprises evaluating at least one sensor signal of the turbocharger arrangement for detecting a failure mode of the sensorless low-pressure turbine bypass valve.
In this way, engine operating parameters may be used to determine a position of the low-pressure turbine bypass valve. If it is determined that the low-pressure turbine bypass valve has degraded, for example if the valve is stuck in a fully open or fully closed position, control of engine boost pressure may be adapted to compensate for the degraded valve. Further, the position of the valve may be determined without using a position sensor, lowering costs and reducing control strategy complexities and resources.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.